1. Field of the invention
This invention relates to a directional control valve (reduction valve) for a pneumatic cylinder.
2. Prior art
For conventional pneumatic cylinders, some shortcomings as described below have been indicated.
When a heavy article is moved downward by utilizing a pneumatic cylinder, the speed for lowering the article is usually controlled by throttling an air outlet of the pneumatic cylinder. At this time, the pressure of the exhausted air is increased, which results in high energy loss.
In the case where the speed of a piston of the pneumatic cylinder is decreased, the area of the air outlet is reduced. If the piston speed is suddenly controlled, bounding of the piston is caused due to the compressibility of air. To prevent such bounding of the piston, a shock absorber is additionally required when the piston is moved at a high speed. Even in this case, an energy loss is caused when the kinetic energy is changed into thermal energy.
Moreover, when the piston is moving at a constant speed, it is difficult to smoothly reduce the speed of the piston from an optional position only by utilizing an air circuit.
Furthermore, bounding of the piston is apt to occur at the moment when the piston starts lowering, and also delay is caused when the piston starts rising.